Such methods for controlling compressors in motor vehicles are known and are intended essentially to avoid overheating of the equipment resulting from overloading. In the case of a compressor for a vehicle with an air suspension system, for example, increased heat generation is less to be feared during normal driving, since fewer level changes normally occur in this state. However, in the case of level changes at standstill, or constant level regulation resulting from manual operation or changing load, or for fast all-terrain vehicles in off-road use or when the compressor or compressor drive is heavily encapsulated with insulation materials (sound damping), relatively severe heating is not uncommon.
In this connection DE 196 21 946 C1, which is incorporated by reference, discloses an air suspension which has a compressor working according to demand and intermittently in normal operation, which compressor is switched on and off by a control unit in dependence on an estimated temperature, the estimated temperature being calculated as the instantaneously present operating temperature. If the calculated “estimated temperature” exceeds a threshold value, the compressor is switched off. As a result, no temperature sensors for monitoring the compressor are needed and therefore no additional signal inputs for the control unit. It is disadvantageous in this case that, also and especially in the case of the abrupt increase in the “estimated value” of the compressor provided each time the compressor is switched on again, which abrupt increase is also disclosed, with rising temperature the compressor is switched on and off more and more frequently and within shorter time intervals, without reaching the desired pressure increase in the system.
In addition, the temperature limit values for switching the compressor on and off in vehicle level control systems are usually designed in such a way that, when the compressor is switched on again, a predefined level change can be carried out with a fully loaded vehicle. However, in most cases a full load is not present, whereby the availability of the compressor is unnecessarily limited.